1. Field of the Invention
This invention relates to medical devices. Particularly, it relates to stent devices and balloon catheter devices. More particularly, it relates to the retentive interactions between these medical devices when they are assembled as stent delivery systems and used in a variety of medical procedures to treat medical conditions in animal and human patients.
2. Description of Related Art
The use of medical devices for treating medical conditions in patients is well known. In particular, medical devices are commonly used during the treatment of vascular conditions involving lesions that block blood flow within body vessels. These procedures usually require that the medical devices be delivered to the treatment site by accessing and tracking through the vessel system.
The medical devices used in these types of procedures include stent delivery systems. Stent delivery systems generally have a stent component (bare metal or drug coated) disposed on the balloon of a balloon catheter component. The stent component must be retained on the balloon during storage and delivery to the treatment site, prior to deployment.
Various methods exist for retaining the stent on the balloon. The most commonly used method is crimping the stent onto the balloon. This is done during a process that is either part of the device manufacture, or it is performed by the physician prior to inserting the stent delivery system within the patient. In general, the stent crimping process involves an inward radial load applied to the stent while it circumferentially encompasses the balloon. The radial load brings the surfaces of the stent and balloon in contact, and the resulting surface friction produces a retaining force. The crimping process usually includes temperature and pressure applied to the stent and balloon surfaces over a period of time. The efficacy of this method is limited by the frictional characteristics of the stent and balloon, as well as by the limits of the pressure and temperature that can be applied without damaging the surface or surface coatings of the stent and balloon. Especially in drug-eluting stents, the polymer drug-containing coatings limit the temperatures and pressures that can be used in the crimping process without significantly damaging coating integrity, coating elution kinetics, and drug potency.
In addition to crimping, means have been developed to improve stent retention during storage and delivery. For instance, features have been provided on the balloon that resists axial movement of the stent. For example, the ends of the balloon have been modified to create pillowed sections with outer diameters approximately the same as the crimped stent diameter. The pillowed balloon section is meant to resist axial movement of the stent by creating an obstruction and reactive load if the stent slides axially during delivery. Similarly, features such as bumps, ridges, and the like have been formed on the balloon to obstruct and resist stent movement. The drawbacks of this method include complicated balloon manufacturing processes, potential weakening of the balloon material, and increased system profile resulting in less deliverability.
An alternative method for improving stent retention involves the use of adhesives to bond the stent to the balloon. This method includes the steps of applying an adhesive to the stent, balloon, or both, and then bringing the component surfaces into contact. The resulting adhesion is intended to resist the dislodgement forces applied during storage and delivery of the stent. The drawbacks of this method include potential weakening of the balloon material, excessive deformation of the stent pattern during deployment, and additional steps during stent delivery and deployment.
Another solution for improving stent retention is to provide a sheath that surrounds the stent. The sheath is removed from the stent prior after delivery to the treatment site and prior to stent deployment. This solution is intended to reduce the dislodgement loads applied to the stent during storage and delivery. The drawbacks of this solution include the requirement for additional delivery steps and the increase in system profile.
The present invention is aimed at improving stent retention while avoiding the shortcomings associated with prior solutions. The object of the present invention is to improve the retention between medical devices by providing a coating on the surface of one medical device that interacts with a coating provided on the surface of another medical device. This invention avoids potential tradeoffs between increased stent retention and issues such as coating integrity, coating elution kinetics, drug potency, weakened balloon material, additional deployment steps, excessive profile, etc., associated with prior solutions.